High Temporal and Spatial Nitrate Variability on an Alaskan Hillslope Dominated by Alder Shrubs

In Arctic ecosystems, increasing temperatures are driving the expansion of nitrogen (N) fixing shrubs across tundra landscapes. The implications of this expansion to the biogeochemistry of Arctic ecosystems is of critical importance, yet many details about the form, location, and availability of N from these shrubs remain unknown. To address this knowledge gap, the spatiotemporal variability of nitrate (NO3−) and its environmental and edaphic controls were investigated at an alder (Alnus viridis spp. fruticosa) dominated permafrost tundra landscape in the Seward Peninsula, Alaska, USA. Soil pore water was collected from locations within alder shrubland growing along a well-drained hillslope and compared to soil pore water collected from locations outside (upslope, downslope, and between) the alder shrubland. δ15N and δ18O of soil pore water were consistent with the predicted range of NO3− produced through microbial degradation of N-rich alder shrub organic matter. Soil pore water collected within alder shrubland had an average NO3− concentration of (4.27 ± 8.02 mg L−1) and differed significantly from locations outside alder shrubland (0.23 ± 0.83 mg L−1; p < 0.05). Temporal variation in NO3− within and downslope of alder shrubland corresponded to precipitation events, where NO3− accumulated in the soil was flushed downslope during rainfall. Enrichment of both δ15N and δ18O isotopes at wetter downslope locations indicate that denitrification buffered the mobility and spatial extent of NO3−. These findings have important implications for nutrient production and mobility in N-limited permafrost systems that are experiencing shrub expansion in response to a warming Arctic.

Vegetation and Glacier Trends in the Area of the Maritime Alps Natural Park (Italy): MaxEnt Application to Predict Habitat Development

Climate change is significantly affecting ecosystem services and leading to strong impacts on the extent and distribution of glaciers and vegetation. In this context, species distribution models represent a suitable instrument for studying ecosystem development and response to climate warming. This study applies the maximum entropy model, MaxEnt, to evaluate trends and effects of climate change for three environmental indicators in the area of the Alpi Marittime Natural Park under the Municipality of Entracque (Italy). Specifically, this study focuses on the magnitude of the retreat of six glaciers and on the distribution of two different plant communities, Alnus viridis scrub and Fagus sylvatica forest associated with Acer pseudoplatanus and tall herbs (megaforbie), in relation to predicted increases in mean temperatures. MaxEnt software was used to model and observe changes over a thirty-year period, developing three scenarios: a present (2019), a past (1980) and a future (2050) using 24 “environmental layers”. This study showed the delicate climate balances of these six small glaciers that, in the next 30 years, are likely to undergo an important retreat (≈−33%) despite the high altitude and important snowfall that still characterize the area. At the same time, it is predicted that the two plant communities will invade those higher altitude territories that, not so long ago, were inhospitable, expanding their habitat by 50%. The MaxEnt application to glaciers has shown to be an effective tool that offers a new perspective in the climate change field as well as in biodiversity conservation planning.

Spatial Distribution of Highland Cattle in Alnus viridis Encroached Subalpine Pastures

Green alder (Alnus viridis) is a shrub species that has expanded over former pastures in Central Europe due to land abandonment, leading to negative agri-environmental impacts, such as a reduction in forage yield and quality and an increase in nitrate leaching. Robust livestock breeds such as Highland cattle could be used to control A. viridis encroachment. The objectives of this study were to investigate the impact of A. viridis encroachment on plant community composition and diversity and to map the spatial distribution of Highland cattle in A. viridis-encroached pastures. During the summer of 2019, three different Highland cattle herds were placed along an A. viridis encroachment gradient. A total of 58 botanical surveys were carried out before grazing to assess plant community composition, pastoral value, and ecological indicator values. The spatial distribution of cattle was studied during the whole grazing period by monitoring six to eight cows equipped with GPS collars in each herd. Plant species associated with higher pastoral values of the vegetation were found in areas with lower A. viridis cover, while highly encroached areas were dominated by a few nitrophilus and shade-tolerant broad-leaved species and by ferns. Cattle spent more time in areas with higher pastoral value but did not avoid areas with high cover of A. viridis, on steep slopes or far from water. These results show that Highland cattle are able to tolerate harsh environmental conditions and that they can exploit A. viridis-encroached pastures. This suggests that they have a high potential to reduce A. viridis encroachment in the long-term.

Ancient CO2 levels favor nitrogen fixing plants over a broader range of soil N compared to present

Small inreases in CO2 stimulate nitrogen fixation and plant growth. Increasing soil N can inhibit nitrogen fixation. However, no studies to date have tested how nitrogen fixing plants perform under ancient CO2 levels (100 MYA), when nitrogen fixing plants evolved, with different levels of N additions. The aim of this study was to assess if ancient CO2, compared to present, favors nitrogen fixers over a range of soil nitrogen concentrations. Nitrogen fixers (Alnus incana ssp. rugosa, Alnus viridis ssp. crispa, and Alnus rubra) and their close non-nitrogen fixing relatives (Betula pumila, Betula papyrifera, Betula glandulosa) were grown at ancient (1600 ppm) or present (400 ppm) CO2 over a range of soil N levels, equivalent to 0, 10, 50, and 200 kg N ha−1 year−1. The growth of non-N fixing plants increased more than N fixing plants in response to the increasing N levels. When grown at an ancient CO2 level, the N level at which non-nitrogen fixing plant biomass exceeded nitrogen fixing plant biomass was twice as high (61 kg N ha−1 year−1) as the N level when plants were grown at the ambient CO2 level. Specific nodule activity was also reduced with an increasing level of soil N. Our results show there was a greater advantage in being a nitrogen fixer under ancient levels of CO2 compared with the present CO2 level.

Ecophysiological Variability of Alnus viridis (Chaix) DC. Green Alder Leaves in the Bieszczady Mountains (Poland)

Alnus viridis (Chaix) DC., green alder, is a fast-growing shrub that grows expansively in the European mountainside. In Poland, A. viridis naturally occurs only in the Bieszczady Mountains (south-eastern part of the country), above the upper forest border. In this study, we assessed the potential of green alder to expand in post-farming areas in the Bieszczady Mountains. We investigated the effects of topographical, climatic, and edaphic characteristics of four various study sites on the physiological and morphological properties of A. viridis leaves in order to answer the question whether the growth of plants in lower positions improves their physiological condition to such an extent that it increases the species invasiveness. This is the first comprehensive ecophysiological study of this species to be carried out in this part of Europe. The photochemical efficiency of PSII, the chlorophyll content, and leaf 13C and 15N discrimination were analyzed. On the basis of leaf radiation reflection, coefficients such as reflectance indices of anthocyanins, carotenoids, flavonoids (ARI2, CRI1, FRI), photochemical index of reflection (PRI), and the water band index (WBI) were calculated. We observed favorable physiological effects in A. viridis plants growing in locations below the upper forest border compared to plants growing in higher locations. As a result, A. viridis may become an invasive species and disturb the phytocoenotic balance of plant communities of the altitudinal zones in the Polish Western Carpathians.

Influența detașării frunzelor asupra acurateței măsurării unor parametri fotosintetici la aninul verde

Fotosinteza este activitatea de bază pe care plantele o realizează având o importanță ridicată în cadrul altor procese cum ar fi: creșterea, acumularea biomasei, cât și procese concurențiale. Măsurarea schimbului de gaze dintre frunză și mediul extern la nivelul coronamentului este o sarcină dificilă din cauza înălțimii arborilor și a imposibilității de a transporta echipamentul la nivelul coronamentului. Acest studiu a testat posibilitatea de a măsura schimbul de gaze pe frunzele detașate, pe frunzele atașate de un lujer detașat și pe frunzele atașate de un lujer detașat, dar introdus într-un recipient cu apă imediat după detașare. Specia pe care s-a efectuat studiul a fost aninul verde (Alnus viridis (Chaix) DC.) datorită înălțimii accesibile și a importanței acesteia în cadrul ecosistemelor montane. În primele două situații, din cauza deficitului de apă la nivelul frunzelor, s-a constatat o scădere a asimilării nete (A), transpirației (E), conductanței stomatale (gsw) la scurt timp după detașare. În a treia situație când lujerul a fost plasat într-un recipient cu apă nu au existat schimbări semnificative privind procesele fotosintetice, parametrii s-au menținut la peste 80% de valoarea inițială.

Ancient CO2 Levels Favor Nitrogen Fixing Plants Over a Broader Range of Soil N Compared to Present

Small inreases in CO2 stimulate nitrogen fixation and plant growth. Increasing soil N can inhibit nitrogen fixation. However, no studies to date have tested how nitrogen fixing plants perform under ancient CO2 levels (100 MYA) when nitrogen fixers evolved, with different levels of N additions. The aim of this study was to assess if ancient CO2, compared to present, favors nitrogen fixers over a range of soil nitrogen concentrations. Nitrogen fixers (Alnus incana ssp. rugosa, Alnus viridis ssp. crispa, and Alnus rubra) and their close non-nitrogen fixing relatives (Betula pumila, Betula papyrifera, Betula glandulosa) were grown at ancient CO2 (1600 ppm) or present CO2 (400 ppm) over a range of soil N levels, equivalent to 0, 10, 50, and 200 kg N ha-1 year-1. The growth of non-N fixing plants increased more than N fixing plants in response to the increasing N levels. When grown at an ancient CO2 level, the N level at which non-nitrogen fixing plant biomass exceeded nitrogen fixing plant biomass was twice as high (61 kg N ha-1 y-1) as the N level when plants were grown at an ambient CO2 level. Specific nodule activity was also reduced with an increasing level of soil N. Our results showed there was a greater advantage in being a nitrogen fixer under ancient levels of CO2 compared with the present CO2 level.